It's true that sometimes, a good villain also is a just tragic villain. It may be someone you rather hate to love, because you know they have to go, leaving you, the player, on a bittersweet note.
Writing a villain you hate is not that easy : he may just turn up annoying. Sometimes, it's just refreshing to have one that only want to see the world burn.
It isn't about a tragic past. It's about his/her motives/reasoning regarding the current situation we are in. If s/he's right (Kreia) then so be it. They're quite one-dimensional if they simply want the world to burn.
You haven't played KotOR2?
Get on it ASAP
http://www.gog.com/game/star_wars_knights_of_the_old_republic_ii_the_sith_lordsAlso get the restored content mod (this is absolutely necessary)
